12.1 ELECTRONS IN ATOMS: IONIZATION ENERGY AND ATOMIC STRUCTURE *DEF’N: IONIZATION ENERGY The ionization energy of an atom is the minimum amount of energy required to remove a mole of ______________ from a mole of ____________ atoms to form a mole of gaseous ions.. i.e. 1st ionization energy: X(g) + IE1 UNITS:______________ 2nd ionization energy: 3rd ionization energy: QUESTION #1. How does the evidence from first ionization energies across periods account for the existence of main energy levels and sub-levels in atoms? *After completing the activity on the backside of this page, re-examine the above graph and then complete the following: i) Which atom has the highest I.E.? Provide an explanation. ii) In general, which atoms tend to have the highest I.E.s? Why? ii) Why is there such a large drop in I.E. after each of the noble gases? What does this suggest in terms of atomic structure? iv) Locate and label the positions of boron, oxygen, aluminum and sulfur on the graph. Identify and provide an explanation of the anomaly. v) Label the following sublevels on the above graph: 1s, 2s, 3s, 4s, 5s and 2p, 3p, 4p, 5p. Complete the following table: PERIOD 1 Element # of electronic protons structure Effective Nuclear Charge econfiguration Orbital Diagram (Valence Shell Only) Ionization Energy (kJ mol-1) H 1312.0 He 2372.3 PERIOD 2 Li 520.2 Be 899.5 *B 800.6 C 1086.5 N 1402.3 *O 1313.9 F 1681.0 Ne 2080.7 PERIOD 3 Na 495.8 Mg 737.7 Al 577.5 Si 786.5 P 1011.8 S 999.6 Cl 1251.2 Ar 1520.6 PERIOD 4 K 418.8 IONIZATION ENERGIES FROM EMISSION SPECTRA (*Solving Problems using E = hv) Recall: (i) To calculate the energy of a photon, E = ____________ can be used. Where: E = ____________________ ; h = _____________________________; v = ____________________ (ii) the wave equation: c = v λ Where: c = the speed of ____________ ; v = _________________ ; λ = ___________________ * Required constants: h = 6.626 x 10-34 J s c = 2.998 x 108 ms-1 SAMPLE PROBLEMS: *If sufficient energy is supplied to the electron in a hydrogen atom, it can be promoted to the infinite level; that is, it can be removed from the atom – it becomes _____________________. This amount of energy corresponds to the energy the electron would emit if it fell back from n = ∞ to n=1, which produces a line in the ______________________ region of the spectrum at a WAVELENGTH OF 91.16 nm. 1. a) Use this wavelength to calculate the amount of energy required to remove this one electron from a hydrogen atom. *Wavelengths must be expressed in _____________ when using the E= hv formula. The calculated answer will be in __________________. b) How much energy, in kJ, is required to remove one mole of electrons?....that is, what is the first ionization energy for hydrogen? PRACTICE: 2. Determine the energy, in J, of a photon of red light, correct to four significant figures, given that the wavelength, λ = 650.0 nm ; (Answer: 3.056 x 10-19 J) QUESTION #2. How do successive ionization energy data relate to the electron configuration of an atom? Example: __________________ *Complete the following: i) What is a logarithmic scale? Why is it used in this example? ii) Identify the largest jumps in energy on the graph. What do each of these jumps correspond with? Explain. iii) Why does the removal of each successive electron, within an energy level, require more energy? iv) Which element is represented in this example? Circle the valence electron(s). On the graph, indicate which orbital each successive electron is removed from. *Explain the following data…in terms of energy levels and valence electrons.